This invention relates to a ventilator for assisting the breathing of a patient who may be paralyzed or sufficiently feeble of muscular strength to require assistance in the breathing action by the generation of pressure in the air flow passing into the patient to assist the inhaling action of the patient.
Ventilators are commonly provided for elderly, infirm or paralyzed patients to assist with breathing. In most cases the ventilator includes a pump for generating the necessary volume of air flow so that the air can be pressurized to be forced into the lungs of the patient during the inhaling action and released by the natural elasticity of the thoracic cavity of the patient in the exhaling action. Subsequent to the replacement of the "iron lung" system of the fiftys and sixties, ventilators have generally employed as a pumping system a reciprocating type pump with a cylindrical chamber and a piston moving axially of the chamber driven by a crank from a rotating shaft. The pump is usually designed to accommodate a maximum volume of air pumped of the order of four to four and a half liters which is the type of volume which would be drawn by a large person breathing vigorously. In order to supply a smaller volume to a smaller patient or a patient during relaxation, the throw of the crank is generally mechanically adjusted to reduce the stroke of movement of the piston within the cylinder.
A pump of this type is generally very heavy, mechanically complex, generates high friction and has high inertia. The pump is therefore suitable for a relatively unsophisticated unit which delivers a substantially fixed amount of air to the patient but cannot respond readily to changes in demand from the patient. In addition the unit is relatively large and heavy and requires a motor of relatively large power and hence the pump is unsuitable for a mobile unit to be driven by battery power.